This invention relates to tie down and release shackles and, more particularly to a ratchet and pawl shackle for securing and releasing vehicles on an automobile transport trailer in which the pawl is shifted laterally to engage and disengage the ratchet wheel, and the like.
To load and secure vehicles for shipment on automobile transport trailers, it has been the practice to use ratchet and pawl devices. Typically, one end of a chain, a cable or the like is temporarily secured to the frame of a vehicle that is to be shipped to a new destination. The other end of the cable is attached to a shaft that also forms the rotatable axle for a ratchet wheel. Thus, as the ratchet wheel is rotated in one direction, the chain is wound on the axle and draws the vehicle to which the chain is attached onto the transport trailer. When the vehicle is drawn into its proper shipment position on the transport trailer, a pawl is pivoted about its own axis of rotation into the gap between two adjoining ratchet teeth in order to prevent the ratchet wheel and the associated axle from turning in the opposite direction and releasing the tension on the chain.
To release the chain tension and thus to permit the ratchet to turn in the opposite direction, the pawl is disengaged from the ratchet wheel by being pivoted in the opposite direction about its axis of rotation to withdraw the pawl from the gap between the two ratchet teeth.
Although this structure satisfies the need to secure vehicles on transport trailers for shipment, it has, nevertheless, several unsatisfactory characteristics. Illustratively, to pivot the pawl out of the gap between two ratchet teeth in order to unload a vehicle from a transporter, a considerable force (usually manual) must be applied to relieve the force on the pawl and pivot the pawl out of engagement with the teeth on the ratchet wheel. The force, for example, that is applied to the pawl must overcome the weight of the vehicle that is being secured, as that weight is reflected in the tension on the chain and the friction force that the chain tension applies to the ratchet wheel at the engaged end of the pawl.
The possibility of a serious injury to a person unloading the vehicle from the transporter in this circumstance is quite clear.
Further in this respect, both the axle for the ratchet wheel and the pivot for the pawl are journalled in a flanged wheel ramp channel. The biasing spring for the pawl is secured to a flange on the side of the ramp channel opposite to the ratchet wheel and the pawl. This flange also provides a bearing that journals one end of the pawl's pivot.
This structure is subject to several difficulties. First, for instance, is the complicated nature of the apparatus which increases the cost of manufacture. The pawl also has a bad characteristic of slipping out of engagement with the ratchet teeth and jamming between the ratchet wheel hub and the channel. Correcting this condition when it occurs is not only burdensome, but it also involves a further risk of personal injury.
From time to time, the biasing spring for the pawl requires replacement. The biasing spring positioned on the side of the channel opposite to the ratchet wheel and the pawl requires dismounting the entire shackle from the transportation trailer, replacement of the spring and then replacing the shackle on the trailer.
Because the pivot for the pawl is journalled both in the channel and in the flange on the opposite side of the channel, the force applied by the ratchet teeth to the pawl also imposes a bending or twisting moment to the pawl's pivot. This bending moment can cause the pawl to disengage the ratchet teeth and allow the ratchet wheel to “free wheel” and release the tie down tension on the vehicle while in transit or at some other undesirable time.